435
FXUS64 KMRX 131551 AAB
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
1151 AM EDT Mon May 13 2024

...New UPDATE...

.UPDATE...
Issued at 1148 AM EDT Mon May 13 2024

Update for wind advisory for much of the far east Tennessee
Mountains and increase chances of showers. Cove Mountain and Camp
Creek observations are reporting winds gusts from 30-35 mph. The
low-level jet per HREF will continue to strengthen through the
rest of the day into the night.

Radar is showing better coverage of light showers across the
central valley due to isentropic lift. Have increased chances of
showers for the rest of the day.

&&

.UPDATE...
Issued at 934 AM EDT Mon May 13 2024

Current forecast looks on track with little to no changes for the
morning update.

Currently light rain or mostly likely sprinkles across southeast
Tennessee and southwest North Carolina. This is due to weak
isentropic lift. For this afternoon into the evening hours, the
low-level jet will strengthen with stronger isentropic upglide
across the area.

At this time, a broader area of rain, mainly light, will spread
across the Tennessee valley and southern Appalachians.

A good deal of mainly mid and high level clouds will spread across
the region keeping cloud cover cloud to mostly cloudy. Best
insolation will be across southwest Virginia and northeast
Tennessee allowing this area to warm the best during the day.

&&

.SHORT TERM...
(Today and tonight)
Issued at 324 AM EDT Mon May 13 2024

Key Messages:

1. Rain chances increase today and tonight as upper low slowly
approaches from the west.

2. Mountain wave conditions develop today and tonight, with gusts
to around 40 mph possible. Uncertainty high enough to preclude
issuing an advisory though.

Discussion:

An upper low was moving into the central plains early this
morning, while a southern stream disturbance was out ahead of
it moving into Louisiana. The vertically stacked system is
forecast to slowly shift eastward over the next 24 hours, perhaps
making it to western Kentucky by the end of the short term
period. Therein lies the uncertainty with the forecast, trying
to get a handle on rain chances and expected rain amounts.
Isentropic analysis shows the forecast area lying between two more
pronounced areas of ascent, one focused just to our south with the
southern stream disturbance and one to our northwest closer to the
upper low. Regional radar imagery shows some weak returns
spreading northeast across northern Alabama this morning, which is
consistent with the leading edge of higher RH and ascent along
the 305K surface. Most guidance brings this into the southern
parts of the CWA by 12z-14z or so. Current radar imagery is less
impressive than models would have you believe but it`s also still
developing. Have a feeling that today is going to be more along
the lines of a high PoP and low QPF type forecast. Tempered the
NBM PoPs with a blend of various models, which lowered them
significantly. This left some areas of likely PoPs in the
mountains this afternoon, with chance values elsewhere. Rain
chances and shower coverage should increase overnight as better
ascent and forcing continue to inch closer.

Another thing to note about today is that H85 flow becomes SSE
today and increases to around 30kt. There`s plenty of support in
various guidance for some mountain wave effects in the wind fields
as a result of this pattern. Will hold off on a wind advisory with
this forecast issuance. Have a few spots where advisory criteria
is met in the forecast across the Smokies, but the stronger H85
wind field will remain to our northwest and even there its only
30-35kt so I`m not confident we`ll hit criteria over the TN
mountains. Certainly we`ll see mountain wave conditions, just not
sure we`ll hit advisory criteria.

&&

.LONG TERM...
(Tuesday through Sunday)
Issued at 324 AM EDT Mon May 13 2024

Key Messages:

1. Showers and thunderstorms continue through Wednesday

2. After a brief break Thursday, another round of storms expected as
we head into the weekend.

Discussion:

At the start of the long term Tuesday, the area`s active week will
already be underway. A trough sweeping across from CO will send a
low pressure center directly for the Tennessee Valley. Something
different that stood out with this system, is maybe better chances
for thunderstorms, as CAPE values are a bit more present than they
have been previous model and forecast runs. New this morning, SPC
has bumped the MRGL for severe a bit to the north which slices our
area approximately north of Knoxville. Cloudiness and temperatures
not all that warm may hamper things a bit, working in our favor. If
we do get any strong to severe storms, damaging winds and large hail
would be the main threats. But I believe the main threat of them all
this week will be flooding, which WPC still hangs onto the MRGL for
FF for parts of our area Tuesday into Wednesday. We will be seeing
multiple rounds of showers and thunderstorms with varying intensity.
Heavier downpours over a certain area will increase the flash
flooding threat.

Activity may wane some overnight into Wednesday, but categorical
PoPs return Wednesday afternoon with increasing instability again.
The slow moving low pressure center and associated upper low will
move to our east switching flow to the northwest. Thursday will try
to dry as high pressure and weak ridging try to build in, however,
wrap-around from the low that just exited the area may send isolated
precip chances to mountainous areas of SW VA and far NE TN.
Elsewhere will be dry and warming into the low 80s.

Come Friday through Sunday becomes a big question mark as agreement
between models decrease with time. A similar tracking system may
impact the area Friday with numerous showers and thunderstorms
possible. Saturday and Sunday is a toss-up between activity from the
Friday system still, additional low pressure development, or just
ridging and drying out. Therefore, isolated to scattered showers and
thunderstorms were kept in the forecast to end the week and long
term period.

&&

.AVIATION...
(12Z TAFS)
Issued at 744 AM EDT Mon May 13 2024

Expect ISOLD SHRA to spread northward across the forecast area
later this morning. Coverage seems like it will less than
previously thought so have trended TAFs towards high res guidance
that suggests a 3hr TEMPO for SHRA should cover it at KCHA and
KTYS. Doubt anything makes it as far north as KTRI. More
widespread SHRA will move in towards the end of the period.
Otherwise, continued moist southerly flow should lead to MVFR CIGS
developing at KTYS and KCHA as well by this evening.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             71  63  76  63 /  50  50  90  70
Knoxville McGhee Tyson Airport, TN  74  60  76  62 /  40  50  80  90
Oak Ridge, TN                       74  60  75  61 /  40  40  80  90
Tri Cities Airport, TN              76  58  76  58 /  20  60  60  80

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...Wind Advisory until 4 AM EDT Tuesday for Blount Smoky Mountains-
     Cocke Smoky Mountains-Sevier Smoky Mountains-Southeast
     Carter-Southeast Greene-Southeast Monroe-Unicoi.

VA...NONE.
&&

$$

SHORT TERM...DH
LONG TERM....KS
AVIATION...CD